This invention relates to circuits and to methods of controlling application of a three-phase supply to an electrical device.
The invention is more particularly, but not exclusively, concerned with ensuring that an electric motor receives the correct phase signals from a three-phase supply.
In many devices driven by a three-phase power supply, it is important that the correct phase outputs are connected to the correct inputs of the device. One example of this is in gyroscope apparatus employing hydrodynamic gas-lubricated bearings which are driven by an electric motor. If the motor is incorrectly connected, the bearings could be rotated in the wrong sense, thereby causing damage.
Although the outputs of three-phase power supplies are generally labelled, it is fairly common for this labelling to be incorrect. Also, despite correct labelling, the electrical device can still be wrongly connected to the power supply. This is especially a problem where the device is being installed by inexperienced technicians.